Production of process gas by heat recovery from low-temperature waste heat

ABSTRACT

Process for heat utilization in steam reforming, having a high-temperature conversion unit, a first heat exchanger, boiler feed water preheater, product condensate heat exchanger, and low-pressure evaporator, a cooling section, in which the process gas is further cooled and a condensate stream is generated and the resultant process gas is passed through at least one unit for further processing. Wherein a first part of the boiler feed water stream is passed into the low-pressure evaporator, and the low-pressure steam generated is divided and a first substream of the low-pressure steam is conducted into the water treatment unit for heat transfer and a second substream of the low-pressure steam is passed to at least one consumer. A second part of the boiler feed water stream is passed via a heat exchanger and one or more boiler feed water preheaters and finally passed for steam generation.

The invention relates to a process for the steam reforming ofhydrocarbonaceous feedstocks, focussing in particular on the productionof process gas by heat recovery from low-temperature waste heat. Theinvention aims at a greater efficiency in exploiting the energy of ahydrogen- and steam-containing process gas produced in a steam reformingprocess. In addition, the invention relates to an apparatus for runningthe process according to the invention.

The steam reforming process serves to convert a reaction mixture ofsteam and hydrocarbonaceous feedstocks into a hydrogen-enriched processgas. This process gas is obtained from the steam reforming process at atemperature above 100° C. In most cases, this temperature ranges between700 and 1000° C.

To allow subsequent processing of the process gas, which, for example,may consist in a treatment and/or an increase of the hydrogen portion bypressure-swing adsorption or a membrane process, it is to be cooled. Inmost cases, the temperature required for subsequent processing rangesbetween 20° and 50° C. Between the individual cooling steps, furtherreaction steps may be provided which, for example, may include thereaction of carbon monoxide with water to give carbon dioxide andhydrogen.

From the patent literature various different approaches are known toexploit the amount of heat contained in the process gas for heatingsubstances involved in and/or outside the process. Frequently the amountof heat contained is specifically used to preheat the boiler feed waterfor the steam reforming process by way of heat exchange.

In a typical conventional heat recovery process integrated into a syngasproduction plant, the amount of heat in the process gas is normally usedby generating a high-pressure steam in a waste-heat boiler in a firststep and converting the process gas in a CO conversion unit into carbondioxide and hydrogen. Subsequently passage through various differentheat exchangers is provided in order to heat, for example, thehydrocarbonaceous feedstock, the boiler feed water and/or the make-upwater. In most cases, the residual heat of the process gas is dissipatedto the atmosphere via a cooling section. The condensate obtained in thecooling section is fed to a water treatment unit, where the make-upwater is added, and then directed to the boiler feed water preheater,from where the heated flow is conveyed to the steam generation system.

The disadvantage involved in this conventional heat recovery method isthat the major part of the heat of the process gas which leaves the COconversion unit is the heat from a moist condensation. This condensationis subject to a pinch effect resulting from further cooling, which makesit very difficult to recover the contained heat and a significantportion is dissipated to the atmosphere via the cooling section. Here,the pinch effect is defined by the approximation of the temperatures oftwo streams, by which the temperature difference between the two streamsis reduced, thus also minimising the driving force for the heatexchange. In this way, a lot of energy from the process gas gets lostunexploited.

A proposal to avoid this problem is disclosed in US 2006/0231463 A1.Here, water is heated and fed to a water treatment unit. A first waterstream from this unit is directed to a low-pressure steam generator anda second water stream to a first boiler feed water preheater. Processgas for heat exchange is passed through both units. The water streamobtained from the first boiler feed water preheater is subdivided intotwo partial streams and sent to two additional boiler feed waterpreheaters, the first of the two, hereinafter referred to as boiler feedwater preheater 1, also being passed by process gas for heat exchange,and the second, hereinafter referred to as boiler feed water preheater2, being passed by flue gas for heat exchange. The two water streamsobtained from the two before-mentioned boiler feed water preheaters arethen conveyed to the steam generation unit.

The disadvantage involved in this system is that the heat exchange inboiler feed water preheater 1 through which process gas is passed issubject to a pinch effect, thus restricting the desired heat transfer toa very limited degree. The general rule applies that the larger theamount of boiler feed water passing through this unit, the higher theuseful heat yield. The subdivision of the water stream before passingthrough boiler feed water preheater 1, however, results in a limitedamount of boiler feed water passing through the unit so that a notableportion of the heat contained in the process gas is dissipated to theatmosphere via the cooling section—usually in the form of aircoolers—and thus gets lost unexploited. In addition, part of the heat ofthe flue gas is used to heat the boiler feed water. This heat portion ofthe flue gas is thus no longer available for the actual steamgeneration.

A further disadvantage involved in the interconnection of the individualunits in US 2006/0231463 A1 is that the water to be heated and then sentto the water treatment unit is to be heated via the amount of heatcontained in the process gas. The water treatment unit usually consistsin a degasifier, which is mostly operated at approximately atmosphericpressure or slight overpressure, typically below 5 bar (abs.), in orderto remove as much oxygen and other gases from the water as possible.Conceptually, the temperature of the water supply stream of this watertreatment unit is typically limited to between 80° and 95° C.Technically, the water supply stream could, however, be heated by theheat contained in the process gas to a temperature above 100° C.Therefore an additional control device must be provided to ensure thatthe temperature of the supply stream to the water treatment unit doesnot exceed the limit of 95° C. In this way, the heat of the process gascannot be exploited completely and the contained residual heat isfinally dissipated unexploited into the atmosphere.

The present invention has been developed against the background of theabove-described state of the art, with the aim to make available aprocess for the production of process gas which does not involve theafore-mentioned problems related to the heat recovery from the amount ofheat contained in the process gas and in which the heat recovery isdesigned even more efficiently. It is also the subject matter of theinvention to disclose an apparatus to run the process according to theinvention.

This is achieved by employing a heat recovery process in the steamreforming of hydrocarbonaceous feedstocks by means of steam, in which asteam reformer generates a process gas which contains a first amount ofheat, and a flue gas which contains a second amount of heat, comprisingat least six heat exchangers, a water treatment unit, a cooling section,a high-temperature conversion unit, at least two pressure boostingunits, at least one consumer and at least one unit for subsequentprocessing of the resulting process gas. The generated process gascontaining the first amount of heat passes the high-temperatureconversion unit, where it is, for the most part, converted into carbondioxide and hydrogen, after which the resulting heat-containing processgas is directed into a first heat exchanger for subsequent heattransfer, and afterwards into at least two more heat exchangers whichare operated as boiler feed water preheaters, product condensate heatexchangers or low-pressure evaporators, and are connected in series inany sequence desired, the process gas resulting from the low-pressureevaporator being first fed into a further boiler feed water preheater,where heat energy is transferred to a partial stream of the boiler feedwater from the water treatment unit, after which the process gasobtained passes the cooling section, where it is further cooledgenerating a condensate flow, and finally fed into at least one unit forsubsequent processing of the resulting process gas.

Furthermore, a deionised water stream is sent to a second heat exchangerfor being heated. The deionised water stream from the second heatexchanger is directed for degassing into the water treatment unit, theboiler feed water stream from the water treatment unit passes a pressureboosting unit and is subdivided, a first part of the boiler feed waterstream being sent to the low-pressure evaporator, where a low-pressuresteam is generated, and the generated low-pressure steam is subdividedand a first partial low-pressure stream is directed for heat transfer tothe water treatment unit and a second partial low-pressure stream issent to at least one consumer. This second partial stream oflow-pressure steam may also be used for preheating other process mediasuch as liquid feedstock or may be transferred for a use outside batterylimit. A second part of the boiler feed water stream is passed throughthe second heat exchanger for the purpose of energy transfer andsubsequently through one or more boiler feed water preheaters for beingheated by the heat amount contained in the process gas and finallyconveyed to the steam generation unit.

In the deaerator of the water treatment unit, the deionised water isdegassed from a major part of the oxygen. Subsequently other dosingfluids may be added as, for example, ammonia for adjusting the pH value.The product resulting from this treatment is referred to as boiler feedwater.

Via a pressure boosting unit, the condensate flow from the coolingsection is passed to the product condensate heat exchanger for beingheated by the heat amount contained in the process gas, after which thecondensate flow is heated again.

The process gas from the first heat exchanger first runs preferablythrough a first boiler feed water preheater, in which heat energy istransferred to a boiler feed water stream, subsequently a productcondensate heat exchanger, where heat energy is transferred to acondensate flow, and from there the resulting process gas is directed tothe low-pressure evaporator, in which low-pressure steam is generatedfrom a boiler feed water stream by means of the heat amount contained,from where it is sent to the subsequent steps of the defined processchain.

In another embodiment of the invention the process gas from the firstheat exchanger first runs through a first boiler feed water preheater,in which heat energy is transferred to a boiler feed water stream,subsequently it is sent to a low-pressure evaporator, in whichlow-pressure steam is generated from a boiler feed water stream by meansof the heat amount contained, and from there the resulting process gasis directed into the product condensate heat exchanger, where heatenergy is transferred to a condensate flow, from where it is sent to thesubsequent steps of the defined process chain.

Advantageously the process gas from the first heat exchanger first runsthrough a product condensate heat exchanger, in which the heat energy istransferred to a condensate flow, from there it runs through the firstboiler feed water preheater, in which heat energy is transferred to aboiler feed water stream, and then it is passed to a low-pressureevaporator, where low-pressure steam is generated from a boiler feedwater stream by means of the amount of heat contained, and subsequentlythe resulting process gas is passed to the subsequent steps of thedefined process chain as described above. In a further embodiment of theinvention the process gas from the product condensate heat exchangerruns first through the first boiler feed water preheater, where heatenergy is transferred to a boiler feed water stream, and then throughanother product condensate heat exchanger, before it is directed intothe low-pressure evaporator, from where it is passed through thesubsequent steps of the defined process chain.

Another possible embodiment of the invention is that the process gasfrom the first heat exchanger runs first through a product condensateheat exchanger, where heat energy is transferred to a condensate flowand to a partial stream of the boiler feed water stream, from where itis passed to the low-pressure evaporator, where low-pressure steam isgenerated from a boiler feed water stream by means of the heat energycontained, and the resulting process gas is then passed to thesubsequent steps of the defined process chain.

Optionally, the process gas leaving the first heat exchanger is sent forsubsequent heat transfer to a further boiler feed water preheater, whichis fed with another partial stream resulting from a further subdivisionof the second part of the boiler feed water stream which has passed thewater treatment unit, the pressure boosting unit and the second boilerfeed water preheater, and is thus further heated.

The process gas leaving the first heat exchanger and/or the furtherboiler feed water preheater is preferably fed into a low-temperatureconversion unit, in which carbon dioxide and hydrogen are formed, fromwhere it is passed to one of the downstream heat exchangers of thedefined process chain.

In a further embodiment of the invention the process gas which has runthrough a heat exchanger is subsequently passed to a separator, and aresulting liquid stream is separated from the heat-containing processgas and united with the condensate flow from the cooling section andfrom other separators, and this mixture is passed via the pressureboosting unit and afterwards through a product condensate heat exchangerfor being heated by the heat contained in the process gas.

Optionally it is further advisable to pass the process gas forsubsequent heat transfer through additional heat exchangers which areintegrated into the process upstream and downstream of the low-pressureevaporator.

The related apparatus for steam reforming of hydrocarbonaceousfeedstocks by means of steam is suited to run a process according toclaim 1, consisting of a sequence of equipment items for the passage ofprocess gas, comprising a high-temperature conversion unit, at leastfour heat exchangers, a cooling section and at least one unit forsubsequent processing of the resulting process gas, wherein conveyinglines are provided to interconnect the individual devices via their gasoutlets and gas inlets to convey the process gas.

The apparatus for steam reforming further comprises another heatexchanger, a water treatment unit, at least two pressure boosting units,at least one consumer, a device for the inlet of a deionised waterstream into the subsequent heat exchanger, a device for transferring thedeionised water stream from the before-mentioned heat exchanger into thewater treatment unit, a device for transferring the boiler feed waterstream leaving the water treatment unit into the pressure boosting unit,a device for subdividing the boiler feed water stream leaving thepressure boosting unit, a first feed line being provided to transport afirst part of the boiler feed water stream to the low-pressureevaporator and a discharge line for removing the generated low-pressuresteam from the low-pressure evaporator, comprising a device fortransferring a first partial stream of the generated low-pressure steamto the water treatment unit and a further device for transferring asecond partial stream of the generated low-pressure steam into thesubsequent consumers, and providing a second feed line for the transportof the second part of the boiler feed water stream to a subsequent heatexchanger, and from there discharging a feed to the second boiler feedwater preheater and from there providing a discharge line to the firstboiler feed water preheater or to a product condensate heat exchangerand/or directly to the subsequent steam generation, and providing adevice for transferring the condensate flow from the cooling section viaa pressure boosting unit into one or more product condensate heatexchangers.

It is of advantage to arrange the sequence of equipment items for thepassage of process gas in a series connection of a high-temperatureconversion unit, a first heat exchanger, a first boiler feed waterpreheater, a product condensate heat exchanger, a low-pressureevaporator, a second boiler feed water preheater, a cooling section andat least one unit for processing the resulting process gas, in the givensequence.

In a further advantageous embodiment of the apparatus, the sequence ofequipment items for the passage of process gas consists in a seriesconnection of a high-temperature conversion unit, a first heatexchanger, a first boiler feed water preheater, a low-pressureevaporator, a product condensate preheater, a second boiler feed waterpreheater, a cooling section and at least one unit for processing theresulting process gas, in the given sequence.

Optionally the sequence of equipment items for the passage of processgas consists in a series connection of a high-temperature conversionunit, a first heat exchanger, a product condensate heat exchanger, afirst boiler feed water preheater, a low-pressure evaporator, a secondboiler feed water preheater, a cooling section and at least one unit forprocessing the resulting process gas, in the given sequence.

Preferably the sequence of equipment items for the passage of processgas consists in a series connection of a high-temperature conversionunit, a first heat exchanger, a product condensate heat exchanger, alow-pressure evaporator, a second boiler feed water preheater, a coolingsection and at least one unit for processing the resulting process gas,in the given sequence, wherein a device for transferring a first partialstream of boiler feed water stream from the second boiler feed waterpreheater into a product condensate heat exchanger is provided as wellas a further device for transferring the second partial stream of boilerfeed water stream from the second boiler feed water preheater directlyto the steam generation.

Another possible embodiment of the invention provides for an additionalthird boiler feed water preheater in the sequence of equipment items forthe passage of process gas, the gas inlet of which is connected to thegas outlet of the first heat exchanger and the gas outlet of which isconnected to the gas inlet of an optional low-temperature conversionunit or a subsequent heat exchanger, and where a device for transferringanother partial stream of boiler feed water from the water treatmentunit and the second boiler feed water preheater ends.

In a further embodiment of the apparatus, a low-temperature conversionunit is integrated into the sequence of equipment items for the passageof process gas, the gas inlet of which is connected to the gas outlet ofthe first heat exchanger or the additional third boiler feed waterpreheater and the gas outlet of which is connected to a subsequent heatexchanger.

It is of advantage that additional separators are integrated into thesequence of equipment items for the passage of process gas, the gasinlets of which are connected to the gas outlets of the respectiveupstream heat exchanger and the gas outlets of which are connected tothe respective heat exchanger downstream in the process chain, and whichare each provided with a discharge line for the produced liquid, whichends into the device for transferring the condensate flow from thecooling section into a product condensate heat exchanger and is passedvia a pressure boosting unit.

In a further embodiment of the invention a second boiler feed waterpreheater is integrated into a separator which is optionally equippedwith additional internals and/or packings and which is provided with adischarge line for conveying the obtained process condensate into thedevice for transferring the condensate flow from the cooling sectioninto a product condensate heat exchanger.

A further embodiment of the apparatus according to the invention is tointegrate further additional heat exchangers into the sequence ofequipment items for the passage of process gas.

It is of advantage to use an air preheating unit as a consumer which isdesigned for the passage of low-pressure steam in order to preheatambient air.

In addition, it is recommended to provide a pressure-swing adsorptionunit or a cooling box as a unit for subsequent processing of theresulting process gas.

Optionally, another device for subdividing the second stream oflow-pressure steam may be provided in addition so to establish a feedline for air-preheating and a feed line to further consumers.

The invention is illustrated below in more detail in an exemplaryfashion by means of seven figures, i.e.:

FIG. 1: shows a process diagram of the process according to theinvention for the recovery of heat from the steam reforming ofhydrocarbonaceous feedstocks by means of steam.

FIG. 2: shows an alternative integration of the heat exchangersrepresented in FIG. 1 into the process for the recovery of heat from thesteam reforming of hydrocarbonaceous feedstocks by means of steam.

FIG. 3: shows another advantageous process variant for the recovery ofheat in the steam reforming of hydrocarbonaceous feedstocks by means ofsteam, in which process gas passes through the product condensate heatexchanger upstream of the first boiler feed water preheater.

FIG. 4: shows another exemplary variant of an interconnection of theheat exchangers used. Here, the major difference as compared to FIGS. 1to 3 is that there is no first boiler feed water preheater.

FIG. 5: supplements the representation of FIG. 1, in which variousoptional elements are integrated into the process such as a third boilerfeed water preheater, a low-temperature conversion unit, an additionaloptional separator and a heat exchanger.

FIG. 6: shows the additional integration of a further product condensateheat exchanger into the process chain according to FIG. 1.

FIGS. 7A to D: show the graphic representation of the temperaturedecrease of the process gas (dashed line) and the heating behaviour ofthe individual media (solid line) by the energy transfer involved in theprocess according to the invention.

FIG. 1 shows a process diagram for the recovery of heat from the steamreforming of hydrocarbonaceous feedstocks by means of steam, in whichthe produced heat-containing process gas 1 a first passes through ahigh-temperature conversion unit 2 where part of the carbon monoxide isconverted to give carbon dioxide and hydrogen. The resultingheat-containing process gas 1 b is then directed to a first heatexchanger 3 for subsequent heat transfer. Subsequently, heat-containingprocess gas 1 c passes through a first boiler feed water preheater 4,where the heat contained in the process gas is transferred to preheatedboiler feed water 14 e which is discharged from water treatment unit 13and has passed through pressure boosting unit 25, heat exchanger 16 andboiler feed water preheater 8. Deionised water 12 a is heated in heatexchanger 16 and the heated deionised water 12 b is sent to watertreatment unit 13 for degassing. If the deionised water is preheated,this involves the advantage that one side of the heat exchanger need tobe designed for low pressures only and part of the heat exchanger maytherefore be fabricated of low-alloy steel, which will save cost. Thisresults in boiler feed water 14 a which is then preheated as describedabove. The resulting boiler feed water stream 14 f is then conveyed tothe steam generation for subsequent processing.

The heat-containing process gas 1 d discharged from boiler feed waterpreheater 4 is subsequently passed to product condensate heat exchanger5 where it transfers heat to process condensate 15 a which has passedpressure boosting unit 27 and been obtained from cooling section 10.Preheated process condensate 15 b is then used for subsequent heating.

Process condensate 15 a is collected by separators of cooling section10, which, in this example, comprises an air cooler and a water cooler,and is reheated in a product condensate heat exchanger 5. This processcould be carried out in a reaction vessel supplied with water, in whichat least part of the steam to be separated from the process gascondenses by direct cooling and is discharged with the water used forcooling. If such a vessel is used, it will be possible to preheat theprocess condensate even further, which would be an advantage, as thehigher the preheating degree of the process condensate the higher theamount of heat in the flue gas used for other media and the steamgeneration.

Heat-containing process gas le resulting from product condensate heatexchanger 5 is subsequently passed to low-pressure evaporator 6 wherethe heat is transferred to part of the boiler feed water stream 14 cgenerated in water treatment unit 13 and has been pressurised.Low-pressure steam 19 a thus obtained is recycled in a first partialstream 19 b to water treatment unit 13, whereas a second partial streamof heated boiler feed water 19 c is fed into a consumer, in this examplean air preheater 18 which serves to heat ambient air 17 which issubsequently used as combustion air 20.

Heat-containing process gas if resulting from low-pressure evaporator 6is subsequently fed into boiler feed water preheater 8 where partialstream 14 d of the boiler feed water generated in water treatment unit13 is further preheated before it is transferred to boiler feed waterpreheater 4. Process gas 1 g resulting from boiler feed water preheater8 then passes cooling section 10 where the process gas is further cooledand a condensate flow produced, and condensate flow 15 a is passed intoproduct condensate heat exchanger 5. Finally the condensedheat-containing process gas 1 h passes through the unit for subsequentprocessing of the resulting process gas 11, which may, for example, be apressure-swing adsorption unit, where the generated hydrogen isseparated from the process gas.

FIG. 2 represents a process variant of FIG. 1. The difference betweenFIG. 2 and FIG. 1 is that heat-containing process gas 1 d which leavesboiler feed water preheater 4 passes first through low-pressureevaporator 6 and subsequently product condensate heat exchanger 5. Theinterconnection of the individual equipment items remains unaffected.The energy recovery of the variant shown in FIG. 1, however, should beexpected to be higher.

A further embodiment is shown in FIG. 3. The difference to FIG. 1 isthat heat-containing process gas 1 c resulting from heat exchanger 3passes through product condensate heat exchanger 5 first and thenthrough boiler feed water preheater 4. The interconnection of theindividual equipment items remains unaffected and is analogous to thesequence of equipment shown in FIG. 1.

In FIG. 4 boiler feed water preheater 4 is completely omitted. Here,heat-containing process gas 1 c obtained from heat exchanger 3 isdirected to product condensate heat exchanger 5, from where theresulting heat-containing process gas 1 d passes through low-pressureevaporator 6 and subsequently boiler feed water preheater 8. Preheatedboiler feed water stream 14 e generated in boiler feed water preheater 8is subdivided in this example and a partial stream 14 f is passed viaproduct condensate heat exchanger 5 together with product condensate 15a, where it is submitted to further preheating. The second partialstream 14 g of the preheated boiler feed water is conveyed to the steamgeneration.

The interconnection shown in FIG. 5 includes further optional equipmentitems of positive effect on the process. Basis for the description andthe specification of differences is FIG. 1. Heat-containing process gas1 c from heat exchanger 3 is passed to an additional boiler feed waterpreheater 21 which is fed from a further partial stream 14 g of theboiler feed water stream, which has been preheated in boiler feed waterpreheater 8. The resulting heated boiler feed water 14 h is alsoconveyed to the steam generation and hence further used. According tothe embodiment shown in this figure, the process water resulting fromboiler feed water preheater 21 is subsequently passed to alow-temperature conversion unit 22 where carbon dioxide and hydrogen areformed. The resulting heat-containing process gas 1 e subsequentlypasses boiler feed water preheater 4 and product condensate preheater 5as shown in FIG. 1. Process gas 1 g resulting from product condensatepreheater 5 is subsequently passed into separator 23, where the obtainedprocess condensate 15 c is separated from the process gas and—with theother process condensate flows—directed as process condensate 15 d via apressure boosting unit 27 to product condensate heat exchanger 5.Furthermore, the resulting heat-containing process gas 1 h passesthrough low-pressure evaporator 6 and separator 7. Condensate flow 15 efrom separator 7 is also sent to product condensate heat exchanger 5together with the other condensate flows 15 d resulting from the overallprocess. Low-pressure steam 19 a resulting from low-pressure evaporator6 is subdivided into three partial streams. Partial stream 19 b of thelow-pressure steam is directed to water treatment unit 13, 19 c to airpreheater 18 and 19 d to subsequent consumers 26. Downstream ofseparator 7 a further heat exchanger 24 is connected and serves foradditional energy transfer. The process continues according to theprocess chain as shown in FIG. 1, consisting of boiler feed waterpreheater 8, cooling section 10 and pressure-swing adsorption unit 11.In this embodiment, however, an additional heat exchanger 9 is providedbetween boiler feed water preheater 8 and cooling section 10.

FIG. 6 shows another variant of FIG. 1. Process condensate flow 15 afrom cooling section 10 is sent via a pressure boosting unit 27 and afurther additional product condensate heat exchanger 28 before it ispassed through product condensate heat exchanger 5. This involves theadvantage that the product condensate absorbs even more heat, which canbe used for heating other media in the subsequent course of the process.

The equipment items additionally integrated in FIG. 5 may be used in acombination as shown in FIG. 5 but may also be integrated as individualcomponents into the respective process chains. In addition, not onlyFIG. 1 may serve as a basis for such equipment integration but allfigures can be used as a basis for the integration. This shows that theprocess involves many options to adapt the respective process to theindividual requirements of a plant operator and also to integrate theappurtenant plant sections into existing plants. Furthermore, it ispossible to implement these process variants in new plants.

In the case of favourable dimensions, the low-pressure evaporator couldbe provided with a safety reserve and, in the event of a shutdown, coolthe process gas by generating and blowing off low-pressure steam. Inaddition to air-preheating and water treatment as described above, thegenerated low-pressure steam may just as well be used to boil out CO₂ ina CO₂ process-gas scrubbing process. The maximum temperature of thegenerated low-pressure steam in such case is 200° C.

Some calculation examples below are used to illustrate the improvementof energy recovery represented as a total from low-pressure steam,boiler feed water and condensate flows. They are based on a typicalinterconnection according to the state of the art, using a minimumnumber of equipment items employed in conventional processes accordingto the state of the art. Based on FIG. 1, low-pressure evaporator 6 isomitted as well as boiler feed water preheater 8 so that boiler feedwater stream 14 d is directly sent into boiler feed water preheater 4.The below tables serve to show how drastically the present inventionpositively influences the energy recovery in comparison to this typicalinterconnection. Some of the before-described figures have been used asa basis for the calculation. It is assumed that there is a separatordownstream of the first four series-connected heat exchangers of thesequence of equipment items for the passage of process gas. Theexemplary calculations are based on a plant capacity of 33,455 Nm³/h ofhydrogen.

Energy recovery: Total from: steam + boiler feed water + productcondensate Interconnection variant [kW] Typical interconnection 10,480FIG. 2 12,670 FIG. 3 13,760 FIG. 6 13,760 As FIG. 3; + integral boilerfeed 13,760 water preheater in separator

From this results that the interconnection variant of the inventionreflected by FIG. 3 and FIG. 6 involves a very high level of energyrecovery as compared to the typical interconnection according to thestate of the art. Consequently, an increase in the total of heatrecovery of approx. 3270 kW can be expected, which would be unused andlost in the typical interconnection variant according to the state ofthe art.

The basic conditions for the calculations are shown in FIGS. 7A to D asa graphic function of temperature and energy recovery. The dashed linerepresents the temperature decrease of the process gas depending on theenergy contained, whereas the solid line represents the heatingbehaviour of the individual media used in the process. The individualprocess steps represented in the graphs are reflected by the insertedreference numbers which are also used in the other FIGS. 1 to 6.

Advantages resulting from the invention:

-   -   Improved energy recovery from the amount of heat contained in        the process gas.    -   Additional preheating of the process condensate in a product        condensate heat exchanger effects that more energy from the flue        gas is available for heating other media and can be used for        steam generation.    -   According to the state of the art the process condensate in the        flue gas duct is preheated until boiling. By preheating the        process condensate by process gas as provided by the invention,        it is possible to do without conventional heating in the flue        gas duct, which will contribute to a simplification of the        process concept.    -   The process according to the invention involves the advantage        that it can be integrated into already existing plants which are        without access to low-pressure steam and must generate it from        valuable high-pressure steam.    -   The temperature and pressure conditions in heat exchanger 16        exclude the risk of steam hammers which contribute to the        improvement of the operational safety.

LIST OF REFERENCES USED

-   1 a, 1 b, 1 c, 1 d, 1 e, 1 f, 1 g, 1 h, 1 i, 1 j, 1 k, 1 l, 1 m, 1 n    Heat-containing process gas-   2 High-temperature conversion unit-   3 Heat exchanger-   4 Boiler feed water preheater-   5 Product condensate heat exchanger-   6 Low-pressure evaporator-   7 Separator-   8 Boiler feed water preheater-   9 Heat exchanger-   10 Cooling section-   11 Pressure-swing adsorption unit-   12 a, 12 b Deionised water-   13 Water treatment unit-   14 a, 14 b, 14 c, 14 d, 14 e, 14 f, 14 g, 14 h, 14 i Boiler feed    water stream-   15 a, 15 b, 15 c, 15 d, 15 e Process condensate-   16 Heat exchanger-   17 Ambient air-   18 Air preheater-   19 a, 19 b, 19 c, 19 d Low-pressure steam-   20 Combustion air-   21 Boiler feed water preheater-   22 Low-temperature conversion unit-   23 Separator-   24 Heat exchanger-   25 Pressure boosting unit-   26 Subsequent consumers-   27 Pressure boosting unit-   28 Product condensate heat exchanger

1. Heat recovery process in the steam reforming of hydrocarbonaceousfeedstocks by means of steam, in which a steam reformer generates aprocess gas which contains a first amount of heat and a flue gas whichcontains a second amount of heat, comprising at least six heatexchangers, a water treatment unit, a cooling section, ahigh-temperature conversion unit, at least two pressure boosting units,at least one consumer and at least one unit for subsequent processing ofthe resulting process gas, in which the generated process gas containingthe first amount of heat passes the high-temperature conversion unit,where it is, for the most part, converted into carbon dioxide andhydrogen, after which the resulting heat-containing process gas isdirected into a first heat exchanger for subsequent heat transfer, andafterwards at least two more heat exchangers which are operated asboiler feed water preheaters, product condensate heat exchangers orlow-pressure evaporators, and are connected in series in any sequencedesired, the process gas resulting from the low-pressure evaporatorbeing first fed into a further boiler feed water preheater, where heatenergy is transferred to a partial stream of the boiler feed water fromthe water treatment unit, after which the process gas obtained passesthe cooling section, where it is further cooled generating a condensateflow, and finally fed into at least one unit for subsequent processingof the resulting process gas, a deionised water stream is sent to asecond heat exchanger for being heated, the deionised water stream fromthe second heat exchanger is directed for degassing into the watertreatment unit, the boiler feed water stream from the water treatmentunit passes a pressure boosting unit and is subdivided, a first part ofthe boiler feed water stream being sent to the low-pressure evaporator,where a low-pressure steam is generated, and the generated low-pressuresteam is subdivided and a first partial low-pressure stream is directedfor heat transfer to the water treatment unit and a second partiallow-pressure stream is sent to at least one consumer, and a second partof the boiler feed water stream being passed through the second heatexchanger for the purpose of energy transfer and subsequently throughone or more boiler feed water preheaters for being heated by the heatamount contained in the process gas and finally conveyed to the steamgeneration, the condensate flow from the cooling section is passed via apressure boosting unit to the product condensate heat exchanger forbeing heated by the heat amount contained in the process gas, afterwhich the condensate flow is heated again.
 2. Process according to claim1, wherein the process gas from the first heat exchanger first runspreferably through a first boiler feed water preheater, in which heatenergy is transferred to a boiler feed water stream, subsequently aproduct condensate heat exchanger, where heat energy is transferred to acondensate flow, and from there the resulting process gas is directed tothe low-pressure evaporator, in which low-pressure steam is generatedfrom a boiler feed water stream by means of the heat amount contained,from where it is passed through the subsequent steps of the definedprocess chain.
 3. Process according to claim 1, wherein the process gasfrom the first heat exchanger first runs through a first boiler feedwater preheater, in which heat energy is transferred to a boiler feedwater stream, subsequently it is sent to a low-pressure evaporator, inwhich low-pressure steam is generated from a boiler feed water stream bymeans of the heat amount contained, and from there the resulting processgas is directed into the product condensate heat exchanger, where heatenergy is transferred to a condensate flow, from where it is passedthrough the subsequent steps of the defined process chain.
 4. Processaccording to claim 1, wherein the process gas from the first heatexchanger first runs through a product condensate heat exchanger, inwhich the heat energy is transferred to a condensate flow, from there itruns through the first boiler feed water preheater, in which heat energyis transferred to a boiler feed water stream, and then it is passed to alow-pressure evaporator, where low-pressure steam is generated from aboiler feed water stream by means of the amount of heat contained, andsubsequently the resulting process gas is passed through the subsequentsteps of the defined process chain.
 5. Process according to claim 4,wherein the process gas from the product condensate heat exchanger runsfirst through the first boiler feed water preheater, where heat energyis transferred to a boiler feed water stream, and then through anotherproduct condensate heat exchanger, before it is directed into thelow-pressure evaporator, from where it is passed through the subsequentsteps of the defined process chain.
 6. Process according to claim 1,wherein the process gas from the first heat exchanger runs first througha product condensate heat exchanger, where heat energy is transferred toa condensate flow and to a partial stream of the boiler feed waterstream, from where it is passed to the low-pressure evaporator, wherelow-pressure steam is generated from a boiler feed water stream by meansof the heat energy contained, and the resulting process gas is thenpassed through the subsequent steps of the defined process chain. 7.Process according to claim 1, wherein the process gas leaving the firstheat exchanger is sent for subsequent heat transfer to a further boilerfeed water preheater, which is fed with another partial stream resultingfrom a further subdivision of the second part of the boiler feed waterstream which has passed the water treatment unit, the pressure boostingunit and the second boiler feed water preheater, and is thus furtherheated.
 8. Process according to claim 1, wherein the process gas leavingthe first heat exchanger and/or the further boiler feed water preheateris fed into a low-temperature conversion unit, in which carbon dioxideand hydrogen are formed, from where it is passed to one of thedownstream heat exchangers of the defined process chain.
 9. Processaccording to claim 1, wherein the process gas which has run through aheat exchanger is subsequently passed to a separator, and a resultingliquid stream is separated from the heat-containing process gas andunited with the condensate flow from the cooling section and from otherseparators, and this mixture is passed via the pressure boosting unitand afterwards through a product condensate heat exchanger for beingheated by the heat contained in the process gas.
 10. Process accordingto claim 1, wherein the process gas for subsequent heat transfer ispassed through additional heat exchangers which are integrated into theprocess upstream and downstream of the low-pressure evaporator. 11.Apparatus for steam reforming of hydrocarbonaceous feedstocks by meansof steam, suited to run a process according to claim 1, consisting of asequence of equipment items for the passage of process gas, comprising ahigh-temperature conversion unit, at least four heat exchangers, acooling section, and at least one unit for subsequent processing of theresulting process gas, conveying lines being provided to interconnectthe individual devices via their gas outlets and gas inlets, and furthercomprising another heat exchanger, a water treatment unit, at least twopressure boosting units, at least one more consumer, a device for theinlet of a deionised water stream into the subsequent heat exchanger, adevice for transferring the deionised water stream from the heatexchanger into the water treatment unit, a device for transferring theboiler feed water stream leaving the water treatment unit into thepressure boosting unit, a device for subdividing the boiler feed waterstream leaving the pressure boosting unit, a first feed line beingprovided to transport a first part of the boiler feed water stream tothe low-pressure evaporator and a discharge line for removing thegenerated low-pressure steam from the low-pressure evaporator,comprising a device for transferring a first partial stream of thegenerated low-pressure steam to the water treatment unit and a furtherdevice for transferring a second partial stream of the generatedlow-pressure steam into the subsequent consumers, and a second feed linebeing provided for the transport of the second part of the boiler feedwater stream to a subsequent heat exchanger, and from there discharginga feed to the second boiler feed water preheater and from thereproviding a discharge line to the first boiler feed water preheater orto one or more product condensate heat exchanger/s and/or directly tothe subsequent steam generation, and a device for transferring thecondensate flow from the cooling section via a pressure boosting unitinto one or more product condensate heat exchangers.
 12. Apparatusaccording to claim 11, wherein the sequence of equipment items for thepassage of process gas consists in a series connection of ahigh-temperature conversion unit, a first heat exchanger, a first boilerfeed water preheater, a product condensate heat exchanger, alow-pressure evaporator, a second boiler feed water preheater, a coolingsection and at least one unit for processing the resulting process gas,in the given sequence.
 13. Apparatus according to claim 11, wherein thesequence of equipment items for the passage of process gas consists in aseries connection of a high-temperature conversion unit, a first heatexchanger, a first boiler feed water preheater, a low-pressureevaporator, a product condensate preheater, a second boiler feed waterpreheater, a cooling section and at least one unit for processing theresulting process gas, in the given sequence.
 14. Apparatus according toclaim 11, wherein the sequence of equipment items for the passage ofprocess gas consists in a series connection of a high-temperatureconversion unit, a first heat exchanger, a product condensate heatexchanger, a first boiler feed water preheater, a low-pressureevaporator, a second boiler feed water preheater, a cooling section andat least one unit for processing the resulting process gas, in the givensequence.
 15. Apparatus according to claim 11, wherein the sequence ofequipment items for the passage of process gas consists in a seriesconnection of a high-temperature conversion unit, a first heatexchanger, a product condensate heat exchanger, a low-pressureevaporator, a second boiler feed water preheater, a second heatexchanger, a cooling section and at least one unit for processing theresulting process gas, in the given sequence, wherein a device fortransferring a first partial stream of boiler feed water stream from thesecond boiler feed water preheater into a product condensate heatexchanger is provided as well as a further device for transferring thesecond partial stream of boiler feed water stream from the second boilerfeed water preheater directly to the subsequent steam generation. 16.Apparatus according to claim 11, wherein an additional third boiler feedwater preheater in the sequence of equipment items for the passage ofprocess gas is provided, the gas inlet of which is connected to the gasoutlet of the first heat exchanger and the gas outlet of which isconnected to the gas inlet of an optional low-temperature conversionunit or a subsequent heat exchanger, and where a device for transferringanother partial stream of boiler feed water from the water treatmentunit and the second boiler feed water preheater ends.
 17. Apparatusaccording to claim 11, wherein a low-temperature conversion unit isintegrated into the sequence of equipment items for the passage ofprocess gas, the gas inlet of which is connected to the gas outlet ofthe first heat exchanger or the additional third boiler feed waterpreheater and the gas outlet of which is connected to a subsequent heatexchanger.
 18. Apparatus according to claim 11, wherein additionalseparators are integrated into the sequence of equipment items for thepassage of process gas, the gas inlets of which are connected to the gasoutlets of the respective upstream heat exchanger and the gas outlets ofwhich are connected to the respective heat exchanger downstream in theprocess chain, and which are each provided with a discharge line for theproduced liquid, which ends into the device for transferring thecondensate flow from the cooling section into a product condensate heatexchanger and is passed via a pressure boosting unit.
 19. Apparatusaccording to claim 11, wherein the second boiler feed water preheater isintegrated into a separator which is optionally equipped with additionalinternals and/or packings and which is provided with a discharge linefor conveying the obtained process condensate into the device fortransferring the condensate flow from the cooling section into a productcondensate heat exchanger.
 20. Apparatus according to claim 11, whereinfurther additional heat exchangers are integrated into the sequence ofequipment items for the passage of process gas.
 21. Apparatus accordingto claim 11, wherein an air preheating unit is used as a consumerdesigned for the passage of low-pressure steam in order to preheatambient air.
 22. Apparatus according to claim 11, wherein apressure-swing adsorption unit or a cooling box is provided as a unitfor subsequent processing of the resulting process gas.